1. Field of the Invention
The present invention relates to electron-emitting devices for emission of electrons, electron sources using them, and image-forming apparatus using the electron sources. The image-forming apparatus according to the present invention can be used in display devices for television broadcasting and the like, display devices of video conference systems, computers, etc., optical printers constructed with use of a photosensitive drum or the like, and so on.
2. Related Background Art
Conventionally, field emission type (FE type) electron-emitting devices configured to apply a strong electric field of not less than 106 V/cm to metal and thereby emit electrons from the metal surface are drawing attention as one of cold electron sources.
If such FE type cold electron sources become practically available, it will become feasible to construct low-profile emissive type image display devices and they will also contribute to reduction in power consumption and reduction in weight.
Known as an example of a vertical FE type is a device in which, as shown in FIG. 13, an emitter 135 is of the shape of a circular cone or a quadrangular pyramid formed from a substrate 131 approximately in the vertical direction; for example, one disclosed in C. A. Spindt, “Physical Properties of thin-film field emission cathodes with molybdenum cones,” J. Appl. Phys., 47, 5248 (1976) or the like (hereinafter referred to as a Spindt type).
On the other hand, a lateral FE structure is shown in FIG. 14. In the figure, numeral 141 designates a substrate, 142 an emitter electrode, 143 an insulating layer, 145 an emitter, 146 an anode, and 147 a profile of an electron beam irradiating the anode. The emitter 145 sharp-pointed at the tip is arranged in parallel with a gate electrode 144 for extracting electrons from the emitter tip, on the substrate and the collector (anode electrode) is disposed above the substrate on which the gate electrode and the emitter electrode are placed (see U.S. Pat. No. 4,728,851, U.S. Pat. No. 4,904,895, and so on).
As an example of the electron-emitting devices using fibrous carbon, Japanese Patent Application Laid-Open No. 8-115652 discloses a configuration in which thermal decomposition is implemented in the presence of organic compound gas on fine particles of catalyst metal whereby fibrous carbon is deposited in a fine gap.
As electroconductive layers for carbon nanotubes, Japanese Patent Application Laid-Open No. 11-194134 and European Patent EP0913508A2 describe metal layers of titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), and molybdenum (Mo). Japanese Patent Application Laid-Open No. 11-139815 describes Si as an electroconductive substrate.
The beam profiles of the electron-emitting devices according to the prior arts will be described referring to FIGS. 13 and 14.
In FIG. 13, which shows the Spindt type electron-emitting device according to the foregoing prior art, numeral 131 denotes the substrate, 132 the emitter electrode, 133 the insulating layer, 134 the gate, and 135 the emitter connected to the emitter electrode 132. When Vf is placed between the emitter 135 and the gate 134, the electric field becomes stronger at the tip of the projection of the emitter 135 and then electrons are emitted from the vicinity of the tip of the cone into the vacuum.
Since the electric field at the tip of the emitter is formed in such a certain finite area as to follow the shape of the emitter tip, the extracted electrons are drawn in the vertical direction relative to the potential from the finite area at the emitter tip.
At this time, electrons are also emitted at various angles. As a result, electrons with large angle components are drawn in directions toward the internal peripheral surface in the hole formed in the gate 134.
As a consequence, where the hole is circular, an electron distribution obtained on the anode 136 in the figure becomes a substantially circular beam profile 137. This indicates that the resultant beam profile is in close relation with the shape of the gate and the distance to the emitter.
The lateral FE configuration as shown in FIG. 14 is the prior art in which electrons are emitted in the aligned extraction direction.
In FIG. 14, numeral 141 designates the substrate, 142 the emitter electrode, 143 the insulating layer, 144 the gate, and 145 the emitter, and the anode 146 is provided on a substrate opposed to the substrate on which the emitter and gate are disposed.
In the case of the lateral FE configuration constructed in this way, some of electrons emitted from the emitter 145 are extracted (or emitted) into the vacuum, but the rest are taken into the gate 144.
In the configuration shown in FIG. 14, the direction of the electric field vector for emission of electrons (the electric field from the emitter 145 toward the gate 144) is different from the direction of the electric field vector toward the anode 146. As a result, the electron distribution (electron beam spot) becomes large.